LIST OF PLATES AND MAPS. PLATES. PLATE I.—Containing Vesuvius or Somma, according to Strabo. To illustrate Chapter XII. Chapter XII. Ground Plan of Rocca Monfina. To illustrate Chapter X. PLATE II.—Town and Castle of Melfi, with Mount Vultur beyond, seen from the N.E. To illustrate Chapter XI. PLATE III.- View of the Town and Castle of Melfi. To illustrate Chapter XI. PLATE IV.-Crater of Mount Vultur from the S.W. To illustrate Chapter XI. MAPS. MAP 1.—Portion of the Kingdom of Naples. Referred to in page 189. in 318 as Plate III. MAP 6.-Chart and Section of Santorino. See page 319. MAP 7.–Palestine and the Dead Sea. Erroneously referred to in page 356 as Plate III. MAP 8.- Peninsula of Kamtschatka. See Chapter XXIII. MAP 9.–Volcanic Band of the Moluccas. See Chapter XXIV. MAP 10.—Volcanic Band of Mexico. See page 476. MAP 11.–United States, marking the site of the principal systems of Thermal Springs. To illustrate pages 554-555 and 589–590. ON VOLCANOS. CHAPTER I. INTRODUCTORY REMARKS. IT cannot fail to be a source of satisfaction to those who, like the Author of this Treatise, have watched with some interest the progress of Geology for more than a quarter of a century, to observe not only the enormous accumulation of facts bearing upon the subject matter of the science itself which have been amassed within that period, but also the advance that has been made in the meanwhile towards the settlement of some of those important problems which stand, as it were, at the very threshold of all inquiries of this description. Thus we need not go further back than to the Geological Essay* of my respected predecessor in the Chair of Chemistry in my own University, to be reminded, that within the last thirty years it was still considered a subject of doubt whether the phænomena, which an examination of the earth's crust had shown to have been manifested in former ages, were the same in kind with any of those that are taking place at present, or whether they involve the supposition of a totally distinct system of causes, which since the commencement of the existing order of things have ceased to operate. The observations made subsequently to the period alluded to, and the discussions that followed in their train, have at * Kidd's Geological Essay, Oxford, 1815. B least so far narrowed the field of controversy, as that the fixity of the laws of nature through all time, as over all space, is regarded as an axiom in all systems of cosmogony, and that the only question upon which any further dispute can arise now is, whether the limited range which our observations embrace, does in fact justify us in pronouncing, that the phænomena which have occurred formerly cannot have exceeded in magnitude and extent those which we see taking place before our eyes. Thus, for instance, instead of vaguely referring, as heretofore, the excavation of valleys and the distribution of erratic blocks to the operation of one universal Deluge, a catastrophe, which if brought about by supernatural agency lies beyond the field of our investigations, and if through the instrumentality of natural agents, would imply a mode of action different from anything we have ever experienced, geologists of the present day are principally occupied in searching for processes now going on, in order to explain the appearances alluded to, and seem only divided as to the question of the possibility of referring them to the action of existing streams, and to such floods as may have occurred in the country within the memory of man, or to the bursting of lakes, the melting of icebergs, the descent of glaciers and other events, which though not observed, at least within the limits of the district under examination, are nevertheless all reducible to the agency of natural forces. The same progress seems to have been made towards the solution of those geological phænomena which depend upon the operation of igneous causes; for whilst, at a period not very remote, the existence of granitic and trappean rocks was referred to processes which, to say the least, implied a mode of action bearing no relation or analogy to anything actually taking place, we are now at least agreed in ascribing such formations to the operation of causes similar to those which at present manifest themselves in volcanos and in earthquakes, modified only by certain differences in the conditions under which these forces were exerted. For the full recognition of this Principle, as well as for the development of the important consequences following from its adoption, we are much indebted to the highly philosophical work of Mr. Lyell, which appeared since the publication of the first edition of this present Treatise, although it may be seen by reference to the latter, that whilst the limited experience I possessed on geological subjects in general would have rendered it an act of presumption on my part to dispute, as Mr. Lyell has done, the conclusions that had been previously arrived at by others with respect to those phænomena which imply the action of water, I had at least stood out for the principle of the unvarying operation of the laws of nature so far as regarded those igneous operations which I had made my principal study. Accordingly the professed object of my Treatise was stated to be that of bringing together from various sources, facts relating to the operation and effects of volcanos and of earthquakes, such as might serve as data by means of which to account for the appearances exhibited by the granitic and trappean rocks produced at former periods of the earth's history. Indeed, even so long ago as the year 1816, when pursuing my studies at Edinburgh, I was led to meditate the excursions which brought me to the above conclusions, and which were undertaken in the first instance principally as a means of ascertaining whether trap rocks were of igneous origin or not. At that period the authority of Professor Jameson, whose lectures I was attending, was calculated to impart to his class a bias in favour of the doctrines of the school of Werner, although I was never so far a convert to the opinions alluded to, as not to entertain misgivings with respect to the conclusions that this geologist and his disciples had in that instance arrived at, and not to feel a persuasion that for the sake of determining whether trap rocks owed their origin to fire, the most effectual method would be that of comparing them in all their details with products universally acknowledged to be volcanic. I perceived that for this purpose a mere examination of hand-specimens was not sufficient—the spots themselves should be visited, and the circumstances of geological position as well the nature of the rocks associated must be carefully compared with what had been observed in those trap districts which had excited so much attention and dispute. I could not help wondering that such an inquiry, intimately connected as it was with the basaltic question, should never have been taken up by any of the zealous supporters of either system; that the volcanos of Auvergne, for instance, should be known to us chiefly through a French work of rather an old date*, or a short German tract of Von Buch’st, and that of the reputed volcanos of Hungary we should possess absolutely no authentic account f, since one author represented the whole country as of aqueous origin g, whilst another described the very craters from whence the lava was ejected |I. A visit to Auvergne in the year 1818 was the first step taken by me towards carrying out the inquiries thus projected, and the result of them was that of speedily bringing me to the conclusions which I stated in my Letters to Professor Jameson, published in his Journal in 1819, and afterwards embodied in my general Treatise on Volcanos, the interval up to the time of the appearance of this latter work in 1826 having been occupied, not so much in hunting for further * Montlosier sur les Volcans d'Auvergne, 1802. + Mineralogische Briefe aus Auvergne, in the 2nd volume of his Geogrostische Beobachtungen, Berlin, 1809. I allude to the winter of 1816-17, which I spent at Edinburgh. In 1819 I visited Auvergne, and published a short account of my observations in Jameson's Journal, vols. iii. and iv. In the same year the first notice of Beudant's researches in Hungary appeared in Daubuisson's . Traité de Géognosie.' They were three years afterwards more fully detailed in his own work, entitled 'Voyage en Hongrie,' from which I have drawn a great part of my account of the structure of the volcanic rocks of that country. In 1820 Professor Buckland examined the Vicentin, and satisfied himself with respect to the analogy which the strata in that country seen alternating with volcanic products bear to the beds above the chalk in England. He also visited Auvergne and part of Hungary. Mr. Bakewell likewise has noticed Auvergne in his • Travels in the Tarentaise, London, 1823. The foreign contributions to the knowledge of volcanos will be seen by reference to my general list of works on the subject. It is to be regretted that the death of Professor Playfair so soon after his return from Italy should have prevented the public from being benefited by his researches in that country. Esmarck, Kurze Beschreibung einer Reise durch Ungarn, 1799. || Fichtel, Mineralogische Bemerkungen von den Karpathen, Wien, 1791. |